Field of the Invention
The present invention relates to a vibration actuator that causes vibrations in an elastic body and that acquires a driving force using the energy of the vibrations, and particularly to a linear vibration actuator.
Description of the Related Art
Several types of vibration actuators (for example, vibration wave motors) that can highly precisely guide and position a member movable with respect to a stator have been developed.
An example of such vibration actuators is a linear vibration wave motor that linearly drives a driven member, as described in Japanese Unexamined Patent Application Publication No. 3-222681 (corresponding to U.S. Pat. No. 5,191,688) (see FIGS. 13A and 13B).
In the existing technology disclosed in Japanese Unexamined Patent Application Publication No. 3-222681, a movable member 602 is disposed to the inner circumference of a cylindrical stator 601 and a linear vibrator 612 is fixed to the stator 601.
A guide portion is provided at a position opposite a slider 603 across the center axis O of the slider 603. The guide portion includes grooves 602a, 602b, and 602c formed in the movable member 602, grooves 601a, 601b, and 601c formed in the stator 601, and guide members 613a, 613b, and 613c. The stator 601 is disposed around the periphery of the movable member 602.
When the linear vibrator 612 is pressed against the slider 603 disposed on the movable member 602, the movable member 602 is positioned so that the center axis of the movable member 602 coincides with the center axis of the stator 601 and accurately driven in the direction of its center axis.
In Japanese Unexamined Patent Application Publication No. 2001-292584 (see FIGS. 14A and 14B), a pressing spring member 717 is disposed between a vibrator 714 and a stationary plate 719, constituting a guide portion, with rubber sheets 716 and 718 interposed between the pressing spring member 717 and the stationary plate 719 and with a rubber sheet 715 interposed between the pressing spring member 717 and the vibrator 714 at or near a vibration node 714a located at a center portion in the longitudinal direction.
Japanese Unexamined Patent Application Publication No. 2001-292584 describes that such a liner vibration wave motor has a simple and small-sized structure while vibrations are not suppressed by the rubber sheet 715.
In Japanese Unexamined Patent Application Publication No. 2009-33969 (corresponding to U.S. Pat. No. 8,018,123) (see FIGS. 15A and 15B), an actuator body 803 is encased in a casing 804 by pushing a second casing 809 into a first casing 808. Support rubber pieces 851 are disposed so as to face both longitudinal end surfaces 836 of a piezoelectric element 830 and an urging rubber piece 852 is disposed so as to face a center portion of the bottom surface of the piezoelectric element 830. Thus, the piezoelectric element 830 is elastically supported by the casing 804.
An ultrasonic actuator having such a configuration has ease of assembly. Moreover, Japanese Unexamined Patent Application Publication No. 2009-33969 describes that the support rubber pieces 851 do not suppress vibrations since the support rubber pieces 851 are elastic bodies although both longitudinal end surfaces 836 of the piezoelectric element 830 function as antinodes of longitudinal vibrations.
In the configuration described in Japanese Unexamined Patent Application Publication No. 3-222681, however, a fast reciprocating movement of the movable member 602 would affect acceleration due to the sudden accelerating and decelerating motion, thereby causing a moment in a pitching direction on the movable member 602 with respect to the direction in which the movable member 602 is moving.
This is a phenomenon that occurs when the center of gravity of the movable member 602 is separated from the position of a portion at which the driving force is generated.
This moment causes a force on some of the guide members 613a, 613b, and 613c in a direction away from the stator 601 or the movable member 602.
When this force exceeds the pressing force with which the linear vibrator 612 and the movable member 602 press against each other, some of the guide members 613a, 613b, and 613c form a gap between themselves and the grooves 601a, 601b, and 601c of the stator 601 or between themselves and the grooves 602a, 602b, and 602c of the movable member 602 at a position near the turning point of the reciprocating movement.
Thus, the guide members 613a, 613b, and 613c repeatedly become separated from or come into contact with the stator 601 or the movable member 602 at startup or interruption, particularly during continuous reciprocating driving, consequently causing noise.
Particularly, when an optical device performs a focusing operation including a wobbling operation in which a focusing lens is brought into focus on the basis of contrast information of a subject by slightly driving the focusing lens forward or backward along the optical axis, unnecessary noise occurs and is undesirably recorded as an audio record.
In Japanese Unexamined Patent Application Publication No. 2001-292584, the vibrator 714 is supported only at the vibration node 714a. The vibrator 714 is thus rotatable in the pitching direction around the node 714a and apt to rotate. The rotation of the vibrator 714 causes a rail 711a, which is a movable member, to rotate and causes a gap between the rail 711a and a rotating member 712. Consequently, noise occurs at the startup and interruption, particularly during continuous reciprocating driving.
Although Japanese Unexamined Patent Application Publication No. 2009-33969 does not clearly describes a pressing unit that presses the actuator body 803 and a stage 811, which is a driven member and illustrated in FIG. 15B, against each other, the stage 811 rotates in the pitching direction when suddenly accelerates or decelerates and similarly causes noise at linear guides formed by rails 812 or the like.